There are many applications where precise movement and/or positioning in one dimension or direction is required while being able to correct for small errors which may occur in one or more additional dimensions. Ideally, it should be possible to correct for errors in all five additional rigid-body dimensions. The long movement may for example be for distances ranging from a fraction of a centimeter (for example 0.5 centimeters) to several ten's of centimeters, with the movements for error correction being for example in the 500 micron range. However, these dimensions, which vary with application, can differ significantly from the examples given.
One such application is to control the scanning mirror in an interferometer. While various flexure, air bearing and other mechanisms are available for performing this actuator function, magnetic bearings offer a number of advantages, particularly for applications in vacuum or low pressure environments such as space satellite instrumentation, and in applications where long life and reliability are critical because of the difficulty in making repairs, space again being an example of such an application. The advantages of magnetic bearings include the absence of friction and wear, and the fact that lubrication is not required. Gas or air bearings, which have many of the same advantages, are not suitable for use in vacuum applications. A magnetic actuator can also be simpler, since it is designed to control multiple degrees of freedom with only a single moving part, whereas complex flexures may be required to accomplish this task in conventional systems.
While many magnetic actuators for moving in a single direction have been provided in the past, and some of these actuators have also had the ability to correct for small positioning errors in dimensions other than that of the long travel, most of these devices have used independent mechanisms for accomplishing these functions and this has limited the magnetic efficiency of the actuators. The elements required for generating the independent flux paths for the two types of motion has also increased the size and weight of such devices, factors which are undesirable in applications such as satellite instrumentation. The independent flux paths have also increased the power requirements for many of these prior art magnetic actuators. Adding redundancy to provide high reliability for space or other applications where servicing of the actuator is difficult or impossible has, because of the design of such actuators, resulted in significant increases in size and weight, and in power requirements.
A need therefore exists for an improved magnetic actuator which permits precise travel over a selected range in a first dimension, while permitting small adjustments to be made in position in at least one and preferably all five additional dimensions, which device has high magnetic efficiency, preferably utilizing the same flux path for the motion in both directions, is relatively compact and light in weight, has relatively low power requirements and can have significant redundancy built in to enhance long term reliability without major increases in the actuator's size, weight or power requirements.